Plasma etching of dielectric layer with etch profile control

ABSTRACT

A semiconductor manufacturing process wherein high aspect ratio deep openings are plasma etched in a dielectric layer using an etchant gas which includes a fluorocarbon, a sulfur-containing gas, an oxygen-containing gas and an optional carrier gas. The etchant gas can include C x F y H z  such as C 4 F 8 , SO 2 , O 2  and Ar. The combination of the sulfur-containing gas and the oxygen-containing gas provides profile control of the deep openings.

FIELD OF THE INVENTION

The present invention relates to an improved method for plasma etching adielectric layer in the fabrication of integrated circuits.

BACKGROUND OF THE INVENTION

A common requirement in integrated circuit fabrication is plasma etchingof openings such as contacts, vias and trenches in dielectric materials.The dielectric materials include doped silicon oxide such as fluorinatedsilicon oxide (FSG), undoped silicon oxide such as silicon dioxide,silicate glasses such as boron phosphate silicate glass (BPSG) andphosphate silicate glass (PSG), doped or undoped thermally grown siliconoxide, doped or undoped TEOS deposited silicon oxide, organic andinorganic low-k materials, etc. The dielectric dopants include boron,phosphorus and/or arsenic. The dielectric can overlie a conductive orsemiconductive layer such as polycrystalline silicon, metals such asaluminum, copper, titanium, tungsten, molybdenum or alloys thereof,nitrides such as titanium nitride, metal silicides such as titaniumsilicide, cobalt silicide, tungsten silicide, molybdenum silicide, etc.

Various plasma etching techniques for etching openings in silicon oxideare disclosed in U.S. Pat. Nos. 4,615,764; 5,013,398; 5,013,400;5,021,121; 5,022,958; 5,269,879; 5,529,657;5,595,627; 5,611,888 and6,159,862. The plasma etching can be carried out in medium densityreactors such as the parallel plate plasma reactor chambers described inthe '398 patent or the triode type reactors described in the '400 patentor in high density reactors such as the inductive coupled reactorsdescribed in the '657 patent. Etching gas chemistries include SF₆, NH₃and an oxidizing component selected from CO₂, O₂, NO, SO₂ and H₂Odescribed in the '764 patent, the oxygen-free, Ar, CHF₃ and optional CF₄gas mixture described in the '121 and '958 patents, the oxygen-free,fluorine-containing and nitrogen gas mixture described in the '879patent, the CF₄ and CO gas mixture described in the '627 patent, theoxygen and CF₄ gas mixture described in the '400 patent, the oxygen, CF₄and CH₄ gas mixture described in the '657 patent, and the Freon and neongas mixture described in the '888 patent. The '862 patent describes abreakthrough procedure using Ar and O₂ or CHF₃ and SO₂ followed byetching SiO₂ using C₅F₈, O₂, a carrier gas and optionally CO.

Techniques to achieve profile control of deep openings having highaspect ratios of at least 5:1 are disclosed in commonly owned U.S. Pat.Nos. 6,117,786 and 6,191,043B1. Of these, the '786 patent describesetching of openings in silicon oxide layers using a gas mixturecontaining fluorocarbon, oxygen and nitrogen reactants wherein theoxygen and nitrogen are added in amounts effective to control theprofile of the etched opening. The '043 patent describes etching of deepopenings 10 to 15 μm deep in a silicon layer by using achlorine-containing etch gas chemistry to etch through a native oxidelayer over the silicon layer and using a gas mixture containing anoxygen reactant gas, helium, an inert bombardment-enhancing gas and afluorine-containing gas such as SF₆, C₄F₈, CF₄, NF₃ and CHF₃ to etchultra deep openings in the silicon layer.

As device geometries become smaller and smaller, it is becomingnecessary to plasma etch deep and narrow openings in silicon oxide.Accordingly, there is a need in the art for a plasma etching techniquewhich achieves such deep and narrow openings. Further, it would behighly desirable to achieve such opening geometries without bowing ofthe sidewalls of the openings.

SUMMARY OF THE INVENTION

The invention provides a process of etching openings in a dielectriclayer with profile control, comprising the steps of supporting asemiconductor substrate having a dielectric layer thereon in a plasmaetch reactor, supplying an etchant gas to the plasma etch reactor,energizing the etchant gas into a plasma state and etching openings inthe dielectric layer, the etchant gas comprising C_(x)F_(y)H_(z) whereinx≧1, y≧1 and z≧0, a sulfur-containing gas and an oxygen-containing gas,the sulfur-containing gas and the oxygen-containing gas being added inamounts effective for profile control of the etched openings.

The etched openings can comprise vias, contacts and/or trenches of adual damascene, a self-aligned contact or self-aligned trench structure.During etching of such openings, the C_(x)F_(y)H_(z) forms a protectivesidewall polymer on the sidewalls of the etched openings, thesulfur-containing gas protects the sidewall polymer from excessiveattack by the oxygen-containing gas and the oxygen-containing gasmaintains a desired thickness of the sidewall polymer. In the case wherethe sulfur-containing gas is SO₂, undissociated SO₂ molecules react withpolymer at the bottoms of the etched openings to prevent etch stop underbombardment of directional ions.

The plasma etch reactor can comprise an ECR plasma reactor, aninductively coupled plasma reactor, a capacitively coupled plasmareactor, a helicon plasma reactor or a magnetron plasma reactor. Forinstance, the plasma etch reactor can comprise a dual frequencycapacitively coupled plasma reactor including an upper showerheadelectrode and a bottom electrode, RF energy being supplied at twodifferent frequencies to either the bottom electrode or at differentfirst and second frequencies to the showerhead electrode and bottomelectrode. In the case where the plasma etch reactor is a capacitivelycoupled plasma reactor, the reactor can have a powered showerheadelectrode and a powered bottom electrode, the showerhead electrode beingsupplied 500 to 3000 watts of RF energy and the bottom electrode beingsupplied 500 to 3000 watts of RF energy.

According to a preferred embodiment, the sulfur-containing gas is SO₂and the oxygen-containing gas is O₂, the SO₂ and O₂ being added inamounts effective to provide undissociated SO₂ molecules which reactwith polymer at bottoms of the etched openings to prevent etch stopunder bombardment of directional ions. The ratio of flow rates of thesulfur-containing gas to the oxygen-containing gas can be 0.5:1 to1.5:1. During the process, pressure in the plasma etch reactor can be 5to 200 mTorr and/or temperature of the substrate support can be −20° C.to +80° C. The etchant gas can include a carrier gas selected from thegroup consisting of He, Ne, Kr, Xe and Ar, the carrier gas beingsupplied to the plasma etch reactor at a flow rate of 5 to 1000 sccm.

The C_(x)F_(y)H_(z) gas can be a mixture of hydrogen-containing andhydrogen-free fluorocarbon gases supplied to the plasma etch reactor ata total flow rate of 5 to 100 sccm. The sulfur-containing gas preferablyconsists of SO₂ and the oxygen-containing gas preferably consists of O₂,each of the SO₂ and O₂ gases being supplied to the plasma etch reactorat a flow rate of 1 to 30 sccm. In the case where the dielectric layeris BPSG, the etchant gas can include SO₂ and O₂ supplied to the plasmaetch reactor with flow rates providing a SO₂:O₂ flow rate ratio of 1:2to 2:1.

In the process of the invention it is possible to obtain etched openings0.30 μm or smaller having substantially straight profiles wherein top,middle and bottom critical dimensions of the openings are substantiallythe same, and the openings have an aspect ratio of at least 5:1. Thedielectric layer can consist of a single material or a stack of layerssuch as low-k materials with or without etch stop layers therebetween.The openings can be etched to depths of at least 2 μm or at least 3 μmand an RF bias can be applied to the semiconductor substrate during theetching step. For example, the etched openings can be 0.25 μm or smallersized openings having substantially straight profiles wherein top,middle and bottom critical dimensions of the openings are substantiallythe same, and the openings have an aspect ratio of at least 10:1.

A preferred etchant gas includes C₄F₈, SO₂, O₂ and Ar supplied to theplasma etch reactor at flow rates of 5 to 30 sccm C₄F₈, 2 to 15 sccmSO₂, 2 to 15 sccm O₂, and 300 to 600 sccm Ar. More preferably, theetchant gas includes C₄F₈, SO₂, O₂ and Ar supplied to the plasma etchreactor at flow rates of 10 to 20 sccm C₄F₈, 4 to 10 sccm SO₂, 4 to 10sccm O₂, and 450 to 550 sccm Ar.

According to one aspect of the invention, the dielectric layer comprisesa doped or undoped silicon dioxide, BPSG, BSG, FSG, PSG, TEOS, thermalsilicon oxide or inorganic low-k material or organic low-k material suchas SiLK. The openings can comprise lines corresponding to a conductorpattern, via openings or contact openings. The openings can be etched inthe dielectric layer so as to have a high aspect ratio such as 3:1 orabove, preferably an aspect ratio of at least 5:1. The fluorocarbonreactant can be one or more hydrogen-free fluorocarbon gases selectedfrom the group of CF₄, C₂F₂, C₂F₄, C₃F₆, C₄F₆, C₄F₈, C₅F₈ and C₆F₆and/or hydrogen-containing fluorocarbon gases such as C₂HF₅, CHF₃, CH₃F,C₃H₂F₆, C₃H₂F₄, C₃HF₅, C₃HF₇, etc. The semiconductor substrate caninclude an electrically conductive or semiconductive layer such as ametal-containing layer selected from the group consisting of Al, Alalloys, Cu, Cu alloys, Ti, Ti alloys, doped or undoped polycrystallineor single crystal silicon, TiN, TiW, Mo, silicides of Ti, W, Co and/orMo or alloys thereof, etc. The optional carrier gas can be selected fromthe group consisting of Ar, He, Ne, Kr, Xe or mixtures thereof. Ifdesired, a stop and/or mask layer such as a silicon nitride, siliconcarbide, silicon oxynitride, or the like can be provided over thedielectric layer and/or between the dielectric and conductive layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an etched dielectric layer wherein deep high aspect ratioopenings have bowed profiles;

FIG. 2 shows an etched dielectric layer wherein deep high aspect ratioopenings have tapered profiles; and

FIG. 3 shows an etched dielectric layer wherein deep high aspect ratioopenings have straight profiles.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a semiconductor manufacturing process whereindeep openings can be plasma etched in dielectric layers while providingdesired profile control. The dielectric layer can comprise silicondioxide, SiLK, BPSG, BSG, FSG, PSG, OSG, and low-k materials. Duringmanufacture of integrated circuits, features such as contacts, vias,conductor lines, etc. are etched in dielectric materials such as oxidelayers. The invention overcomes a problem with prior etching techniquesby increasing profile control during etching of deep openings havinghigh aspect ratios.

The invention provides a process for plasma etching 0.3, especially 0.25μm and smaller high aspect ratio features such as vias and contacts insilicon oxide layers on semiconductor substrates. In the process, a gasmixture containing fluorocarbon, sulfur and oxygen reactants isenergized into a plasma state and during the etching process the sulfurand oxygen synergistically react to prevent polymer build-up fromcausing a phenomenon known as “etch stop.” Etch stop is a problem whichoccurs during plasma etching of deep and narrow openings in siliconoxide using gas chemistries which form too much polymer, i.e.,polymer-build-up in the opening prevents further etching of the siliconoxide. In the process of the invention, the polymer build-up can bereduced by the synergistic effect of breaking up the polymer with theoxygen and sulfur in the etching gas mixture.

According to the invention, oxygen- and sulfur-containing gases areadded in amounts effective to control the profile of the etched opening.For instance, by adjusting the amount of sulfur relative to the amountof oxygen it is possible to form straight openings. On the other hand,by decreasing or eliminating oxygen in the etching gas mixture it ispossible to form tapered openings. As an example, a tapered openingvarying in size from 0.3 μm at the top to 0.1 μm at the bottom can beformed using an oxygen-free etching gas mixture of C₄F₈, Ar and SO₂. Forstraight openings, the preferred amount of the oxygen-containing gas is50 to 200%, more preferably 75 to 125% of the amount of thesulfur-containing gas. However, it is advantageous if the amount of theoxygen-containing gas is higher for dielectric layers less dopantadditions.

The oxygen-containing gas can be supplied to the plasma etching reactorin amounts effective to cut through polymer at the bottom of the etchedopening. For a reactor which forms a medium density plasma, in the casewhere the oxygen-containing gas comprises O₂, the O₂ can be supplied tothe reactor at a flow rate of 1 to 30 sccm, preferably 3 to 15 sccm. Inthe case where the sulfur-containing gas comprises SO₂, the SO₂ can beadded at a flow rate of 1 to 30 sccm, preferably 3 to 15 sccm. Thecarrier gas preferably comprises Ar which can be added at a flow rate of10 to 1000 sccm, preferably 100 to 750 sccm.

In order to obtain openings with straight sidewalls it is desirable tocontrol the oxygen addition such that enough polymer is present to avoidor minimize bowing and enough polymer is removed to avoid the etch stopphenomenon. With respect to polymer removal, the effect of the oxygen isbalanced by the sulfur addition. For instance, when using SO₂ it ispossible to provide adequate sidewall passivation of the etched opening,i.e., provide polymer buildup of a desired thickness. Accordingly, byselectively adjusting the O₂ and SO₂ flow rates it is possible to obtainstraight and narrow high aspect ratio openings.

The etching gas mixture preferably includes an inert carrier gas. Argonis an especially useful inert carrier gas which aids fluorine inattacking the silicon oxide. However, other inert gases such as He, Ne,Kr and/or Xe can be used as the carrier gas. In the case of using a highdensity etch reactor operated at low chamber pressures, to maintain thedesired pressure in the plasma etching reactor it is preferable tocontrol the amount of carrier gas introduced into the reactor to be atlower levels while still maintaining the plasma. For a medium densityplasma reactor, however, argon can be supplied at higher rates into thereactor in amounts of 150 to 300 sccm. The carrier gas preferably aidsthe oxide etching rate due to sputtering of the oxide.

The fluorocarbon can be hydrogen-free and/or contain hydrogen. Theamount of fluorocarbon gas to be supplied to the plasma reactor shouldbe sufficient to achieve the desired degree of polymerizing. As anexample, in a medium density plasma reactor, the total fluorocarbon gascan be supplied in amounts of 3 to 100 sccm, preferably 5 to 25 sccm,and more preferably 10 to 20 sccm.

The process of the invention is useful for obtaining extremely highaspect ratios of at least 5:1, preferably 10:1 and more preferably 20:1or higher. The process is especially useful for obtaining aspect ratiosup to 10:1 for openings smaller than 0.3 μm. For example, it is possibleto obtain straight walls for 0.25 μm openings at depths greater than 2.1μm.

The reactor pressure is preferably maintained as low as possible. Ingeneral, too low a reactor pressure can lead to plasma extinguishmentwhereas too high a reactor pressure can lead to the etch stop problem.For medium density plasma reactors such as a dual frequency capacitivelycoupled etch reactor, the reactor is preferably at a pressure below 200mTorr such as 20 to 40 mTorr. Due to plasma confinement at thesemiconductor substrate undergoing etching, the pressure at thesubstrate surface may range from 30 to 100 mTorr, e.g., 45 to 65 mTorr.

The substrate support supporting the semiconductor substrate undergoingetching preferably cools the substrate enough to prevent burning of anyphotoresist on the substrate, e.g., maintain the substrate below 140° C.In medium density plasma reactors, it is sufficient to cool thesubstrate support to a temperature of −20 to +80° C. In a dual plateplasma reactor or triode type reactor, the substrate support cancomprise a bottom electrode such as an ESC on which a substrate such asa silicon wafer is electrostatically clamped and cooled by supplyinghelium at a desired pressure between the wafer and top surface of theESC. In order to maintain the wafer at a desired temperature of, forexample, 60 to 120° C., the He can be maintained at a pressure of 2 to30 Torr in the space between the wafer and the chuck.

The plasma reactor preferably comprises a medium density parallel plateor triode type plasma reactor. In such reactors, it is desirable tomaintain the gap between the top electrode and the bottom electrodesupporting the semiconductor substrate at a distance of about 1.3 to 2.5cm. The total power supplied to the top and bottom electrodes can be inthe range of about 1000 to 4000 watts.

The process of the invention is applicable to etching of variousdielectric layers such as doped silicon oxide such as fluorinatedsilicon oxide (FSG), undoped silicon oxide such as silicon dioxide,spin-on-glass (SOG), silicate glasses such as boron phosphate silicateglass (BPSG) and phosphate silicate glass (PSG), doped or undopedthermally grown silicon oxide, doped or undoped TEOS deposited siliconoxide, low-k dielectrics including inorganic materials and organicpolymer materials, etc. The dielectric dopants include boron, phosphorusand/or arsenic. The dielectric can overlie a conductive orsemiconductive layer such as polycrystalline silicon, metals such asaluminum, copper, titanium, tungsten, molybdenum or alloys thereof,nitrides such as titanium nitride, metal silicides such as titaniumsilicide, cobalt silicide, tungsten silicide, molybdenum silicide, etc.A silicon nitride layer can be provided over the dielectric layer and/orbetween the dielectric and conductive/semiconductive layers.

The plasma can be produced in various types of plasma reactors. Suchplasma reactors typically have energy sources which use RF energy,microwave energy, magnetic fields, etc. to produce a medium to highdensity plasma. For instance, a high density plasma could be produced ina transformer coupled plasma (TCP™) available from Lam ResearchCorporation which is also called inductively coupled plasma reactor, anelectron-cyclotron resonance (ECR) plasma reactor, a helicon plasmareactor, or the like. An example of a high flow plasma reactor which canprovide a high density plasma is disclosed in commonly owned U.S. Pat.No. 5,820,261, the disclosure of which is hereby incorporated byreference. The plasma can also be produced in a parallel plate etchreactor such as the dual frequency plasma etch reactor described incommonly owned U.S. Pat. No. 6,090,304, the disclosure of which ishereby incorporated by reference.

In one embodiment, the invention provides a process for plasma etchinghigh aspect ratio features such as conductor lines, vias and contactsincluding self aligned contacts (SAC) in dielectric layers onsemiconductor substrates. In the process, a gas mixture containingfluorocarbon, oxygen, sulfur dioxide and optional gases such as acarrier gas (e.g., argon) is energized in a plasma etch reactor into aplasma state such that the fluorocarbon, the oxygen and sulfur dioxidereactants are at least partially dissociated. During the etchingprocess, the dielectric layer is etched by fluorine containing speciesand the carbon forms a protective polymer on sidewalls of the etchedopenings. The oxygen and sulfur dioxide cooperate to balance polymerbuild-up sufficiently to protect sidewalls of etched features whileavoiding pinch-off and etch stop problems due to excessive polymerbuild-up. In general, sulfur dioxide can be used to react with bottompolymer in the etched openings and the oxygen is added in an amountsufficient to control polymer buildup on the sidewalls of the etchedopenings. For etching deep and narrow openings in BPSG, for instance, ithas been found desirable to add SO₂ and O₂ in about the same flow rates.For etching less doped materials such as undoped silicon dioxide, theSO₂ can be supplied at a lower flow rate than the O₂.

The ratio of oxygen to sulfur dioxide is preferably controlled to takeinto account the size of the features being etched and the filmcomposition of the material being etched. For instance, when etchinglarger feature sizes less sulfur dioxide is needed to protect thesidewalls of the etched openings. For dielectric materials which aresofter due to doping of the material more sulfur dioxide can be used toprovide greater sidewall protection. The advantageous effects of theinvention can be achieved by supplying the oxygen reactant andfluorocarbon reactant to plasma etching reactor at a flow rate ratio ofoxygen reactant to fluorocarbon reactant of 1.5 or less. For selectiveetching of BPSG in a medium density plasma etch reactor, the flow rateratio of oxygen reactant to fluorocarbon reactant is preferably 0.25 to0.75.

The fluorocarbon is preferably hydrogen-free and may comprise at leastone of CF₄, C₂F₂, C₂F₄, C₃F₆, C₄F₆, C₄F₈, C₅F₈, C₆F₆, etc. The etchinggas mixture may optionally include other gases and/or an inert carriergas such as argon (Ar), helium (He), neon (Ne), krypton (Kr), xenon (Xe)and mixtures thereof. Argon is an especially useful inert carrier gaswhich aids fluorine in attacking dielectric materials such as siliconoxide. The argon can be supplied into the reactor in amounts of 0 to1000 sccm, preferably 100 to 750 sccm. The carrier gas preferably aidsthe dielectric etch rate, e.g., the oxide etching rate can be increaseddue to sputtering of the oxide.

The amount of fluorocarbon gas to be supplied to the plasma reactorshould be sufficient to achieve the desired degree of polymerizing.Oxygen and fluorocarbon reactants can each be supplied at flow rates of5 to 100 sccm, preferably 5 to 50 sccm, and more preferably 5 to 20sccm. As an example, the oxygen reactant flow rate can range from 5 to20 sccm when C_(x)F_(y) is supplied at 10 to 20 sccm, and argon, ifsupplied, can range from 100 to 600 sccm. In another example, theC_(x)F_(y) is C₄F₆, the oxygen containing gas is O₂ and the C₄F₆ and O₂are supplied to the plasma etch reactor at flow rates having a ratio ofC₄F₆:O₂ of 1:1 to 2:1. In an additional example, the C₄F₆ and O₂ aresupplied to the plasma etch reactor at flow rates to avoid etch stopduring etching of the openings in a SAC or dual damascene structure. TheO₂ can be supplemented or replaced with other oxygen containing gasessuch as CO. For instance, CO can be added to the etch gas at a flow rateof 50 to 500 sccm.

It will be apparent to those skilled in the art that the flow rates ofthe various gases will depend on factors such as the size of thesubstrate, the type of plasma reactor, the power settings, the vacuumpressure in the reactor, the dissociation rate for the plasma source,etc.

The process of the invention is useful for obtaining extremely deep andnarrow openings with aspect ratios of at least 10:1, the process beingespecially useful for obtaining aspect ratios up to 10:1 for openingssmaller than 0.3 μm, preferably as small as 0.18 μm and below. Forexample, in one embodiment, a dual frequency plasma etch reactor (suchas the dual frequency plasma etch reactor described in commonly ownedU.S. Pat. No. 6,090,304, the disclosure of which is hereby incorporatedby reference) was operated with a top electrode power of 0 to 5000watts, preferably 1000-2000 watts, and a bottom electrode power of 0 to5000 watts, preferably 1000-2000 watts. For example, straight 0.25 μmopenings having depths of about 3 μm can be etched in about 4 minutes ina single step with the chamber pressure set at about 30 mTorr, one orboth of the electrodes powered with 1400 watts at 27 MHz and 1800 wattsat 2 MHz, using an etch gas mixture of 500 sccm Ar, 6 sccm O₂, 6 sccmSO₂, and 15 sccm C₄F₈. Similar profiles could be obtained by increasingthe O₂ and SO₂ flow rates while maintaining a flow rate ratio of about1:1 or by increasing the O₂ flow rate with respect to the SO₂ flow rate,e.g., 9 sccm O₂ and 4.5 sccm SO₂.

FIG. 1 illustrates the bowed etch profile obtained when using an etchgas mixture which includes O₂ but not SO₂ and FIG. 2 illustrates thetapered etch profile obtained when the etch gas mixture includes SO₂ butnot O₂. In FIG. 1, a dielectric layer 2 having bowed openings 4 wasobtained when the dielectric etch was carried out for about 4 minutes ina single step with the chamber pressure set at about 50 mTorr, one orboth of the electrodes powered with 500watts at 27 MHz and2000 watts at2 MHz, 500 sccm Ar, 7 sccm O₂, and 15 sccm C₄F₈. In FIG. 2, a dielectriclayer 6 having tapered openings 8 was obtained when the dielectric etchwas carried out an oxide etch can be carried out for about 4 minutes ina single step with the chamber pressure set at about 30 mTorr, one orboth of the electrodes powered with 1400 watts at 27 MHz and 1800 wattsat 2 MHz, 500 sccm Ar, 13 sccm SO₂, and 15 sccm C₄F₈. FIG. 3 shows anexample of a dielectric layer 10 having straight openings 12, theopenings being etched in accordance with the process according to theinvention.

The reactor pressure is preferably maintained at a level suitable forsustaining a plasma in the reactor. In general, too low a reactorpressure can lead to plasma extinguishment whereas in a high densityetch reactor too high a reactor pressure can lead to the etch stopproblem. For high density plasma reactors, the reactor is preferably ata pressure below 30 mTorr, more preferably below 10 mTorr. For mediumdensity plasma reactors, the reactor is preferably at a pressure from 20to 100 mTorr. Due to plasma confinement at the semiconductor substrateundergoing etching, the vacuum pressure at the substrate surface may behigher than the vacuum pressure setting for the reactor.

The substrate support supporting the semiconductor substrate undergoingetching preferably cools the substrate enough to prevent deleteriousside reactions such as burning of any photoresist on the substrate andformation of undesirable reactant gas radicals. In high and mediumdensity plasma reactors, it is sufficient to cool the substrate supportto a temperature of −20 to +80° C. The substrate support can include abottom electrode for supplying an RF bias to the substrate duringprocessing thereof and an ESC for clamping the substrate. For example,the substrate can comprise a silicon wafer which is electrostaticallyclamped and cooled by supplying helium (He) at a desired pressurebetween the wafer and top surface of the ESC. In order to maintain thewafer at a desired temperature of the He can be maintained at a pressureof 10 to 30 Torr in the space between the wafer and the chuck.

The foregoing has described the principles, preferred embodiments andmodes of operation of the present invention. However, the inventionshould not be construed as being limited to the particular embodimentsdiscussed. Thus, the above-described embodiments should be regarded asillustrative rather than restrictive, and it should be appreciated thatvariations may be made in those embodiments by workers skilled in theart without departing from the scope of the present invention as definedby the following claims.

What is claimed is:
 1. A method of etching openings in a dielectriclayer with profile control, comprising: supporting a semiconductorsubstrate in a plasma etch reactor, the substrate including a dielectriclayer; supplying an etchant gas to the plasma etch reactor; and etchingopenings in the dielectric layer by energizing the etchant gas into aplasma state, the etchant gas comprising C_(x)F_(y)H_(z) wherein x≧1,y≧1 and z≧0, SO₂ gas and an oxygen-containing gas, the SO₂ gas and theoxygen-containing gas being added in amounts effective for profilecontrol of the etched openings.
 2. The method of claim 1, wherein theopenings comprise vias, contacts, and/or trenches of a dual damascene,self-aligned contact or self-aligned trench structure.
 3. The method ofclaim 1, wherein the C_(x)F_(y)H_(z) forms a protective sidewall polymeron sidewalls of the etched openings, the SO₂ gas protects the sidewallpolymer from excessive attack by the oxygen-containing gas and theoxygen-containing gas maintains a thickness of the sidewall polymereffective for profile control of the etched openings.
 4. The method ofclaim 1, wherein the plasma etch reactor comprises an ECR plasmareactor, an inductively coupled plasma reactor, a capacitively coupledplasma reactor, a helicon plasma reactor or a magnetron plasma reactor.5. The method of claim 1, wherein the plasma etch reactor comprises adual frequency capacitively coupled plasma reactor including an uppershowerhead electrode and a bottom electrode, RF energy being supplied attwo different frequencies to either the bottom electrode or at differentfirst and second frequencies to the showerhead electrode and bottomelectrode.
 6. The method of claim 1, wherein the oxygen-containing gasis O₂, the SO₂ and O₂ being added in amounts effective to provideundissociated SO₂ molecules which react with polymer at bottoms of theetched openings to prevent etch stop under bombardment of directionalions.
 7. The method or claim 1, wherein the ratio of flow rates of theSO₂ gas to the oxygen-containing gas is 0.5:1 to 1.5:1.
 8. The method ofclaim 1, wherein pressure in the plasma etch reactor is 5 to 200 mTorrand/or temperature of the substrate support is −20° C. to +80° C.
 9. Themethod of claim 1, wherein the plasma etch reactor is a capacitivelycoupled plasma reactor having a powered showerhead electrode and apowered bottom electrode, the showerhead electrode being supplied 500 to3000 watts of RF energy and the bottom electrode being supplied 500 to3000 watts of RE energy.
 10. The method of claim 1, wherein the etchantgas includes a carrier gas selected from the group consisting of He, Ne,Kr, Xe and Ar, the carrier gas being supplied to the plasma etch reactorat a flow rate of 5 to 1000 sccm.
 11. The method of claim 1, wherein thedielectric layer comprises a doped or undoped silicon dioxide, BPSG,BSG, FSG, PSG, TEOS, thermal silicon oxide or inorganic low-k materialor organic low-k material, the dielectric layer overlying a conductivelayer selected from the group consisting of Al, Al alloys, Cu, Cualloys, Ti, Ti alloys, doped or undoped polycrystalline or singlecrystal silicon, TiN, TiW, Mo, silicides of Ti, W, Co and/or Mo oralloys thereof, the semiconductor substrate including an optional stoplayer and/or mash layer selected from silicon nitride, silicon carbideor silicon oxynitride over the dielectric layer and/or between thedielectric and conductive layer.
 12. The method of claim 1, wherein theoxygen-containing gas is O₂, each of the SO₂ and O₂ gases being suppliedto the plasma etch reactor at a flow rate of 1 to 30 sccm.
 13. Themethod at claim 1, wherein the dielectric layer is BPSG and the etchantgas includes SO₂ and O₂ supplied to the plasma etch reactor with flowrates providing a SO_(2:) O₂ flow rate ratio of 1:2 to 2:1.
 14. Themethod of claim 1, wherein the etched openings are 0.30 μm or smallersized openings having substantially straight profiles wherein top,middle and bottom critical dimensions of the openings are substantiallythe same, and the openings have an aspect ratio of at least 5:1.
 15. Themethod of claim 1, wherein the dielectric layer includes a stack oflayers of low-k materials with or without etch stop layers therebetween,the openings being etched to depths of at least 2 μm.
 16. The method ofclaim 1, wherein an RF bias is applied to the semiconductor substrateduring the etching step.
 17. The method of claim 1, wherein the etchedopenings are 0.25 μm or smaller sized openings having substantiallystraight profiles wherein top, middle and bottom critical dimensions ofthe openings are substantially the same, and the openings have an aspectratio of a least 10:1.
 18. The method of claim 1, wherein the etchantgas includes C₄F₈SO₂, O₂ and Ar supplied to the plasma etch reactor atflow rates of 5 to 30 sccm C₄F₈, 2 to 15 sccm SO₂, 2 to 15 sccm O₂, and300 to 600 sccm Ar.
 19. The method of claim 1, wherein the etchant gasincludes C₄F_(8,) SO₂, O₂ and Ar supplied to the plasma etch reactor atflow rates of 10 to 20 sccm C₄F₈, 4 to 10 sccm SO₂, 4 to 10 sccm O₂, and450 to 550 sccm Ar.
 20. The method of claim 1, wherein C_(x)F_(y)H_(z)comprises at least one hydrogen-free fluorocarbon selected from CF₄,C₂F₂, C₂F₄, C₃F₆, C₄F₆, C₄F₈ and C₆F₆ and/or at least one hydrogencontaining fluorocarbon selected from C₂HF₃, CHF₃, CH₃F, C₃H₂F₀, C₃H₂F₄,C₃HF₅, C₃HF₇.